Mitigating the Effects of Shock and Vibration in Military Applications

In the defense industry, critical electronic systems in battlefield equipment are routinely exposed to extreme levels of shock and vibration. Continuous operation under the most severe environmental conditions is an unyielding requirement. Electronics chassis manufacturers must incorporate design features that ensure maximum payload protection and the highest performance levels.

Systems in ground vehicles, aircraft and ships are subject to variants of shock and vibration particular to the normal operating conditions encountered by each asset type. On board electronics must operate successfully while traveling over terrain, navigating across rough seas and flying through extreme turbulence. In addition, systems must perform without fail in specific vibration environments that are associated with ground vehicle engines, helicopter and winged aircraft propellers, shipboard propellers and rotating machinery as well as jet engines. Systems mounted in close proximity to on-board munitions must stand up to the high levels of gunfire shock and vibration. 

Shock and Vibration

Shock in the defense industry refers to a sudden and extreme force or impact that can cause severe damage to equipment, vehicles or personnel. In battle, shock is generally caused by explosions from incoming enemy fire and collisions, it can also be caused by the rough handling of equipment during transport.

Vibration is the continuous oscillatory motion or repetitive motion that can occur at various frequencies and magnitude created by the same types of environments.

MIL-STD 810 and 901 are the two dominant standards mandated by the Department of Defense (DoD) for use in testing electronic equipment against damage due to effects of shock and vibration. Each standard defines detailed methods for creating and testing against the specific shock and vibration conditions for every application. The systems under test are mounted to shock and vibration tables which mimic the magnitude, frequency, direction and duration of disturbances anticipated in the battle space.

Ruggedization – Inside and Out

For electronic systems in rugged VITA 48.2 conduction cooled ATR chassis designed for VPX and SOSA aligned board architectures, shock and vibration resistance takes place both inside and outside of the chassis at the packaging level.

Chassis Design

VITA 48.2 REDI (Ruggedized Enhanced Design Implementation) defines 3U VPX boards for conduction cooled systems and is primarily intended to address thermal management issues. VITA 48.2 boards are encased in aluminum housings and are each locked tightly into aluminum chassis rails to ensure maximum conductance to the chassis structure. This hard casing, along with mechanical locking features, yields a secondary benefit by eliminating board vibration. This prevents connector and component fatigue over the life of the system. Chassis design must also ensure that internal cabling is properly routed and stabilized to prevent movement or connection stress that may induce failures in connectivity.

LCR’s ATR chassis for VITA 48.2 payloads provide exceptional protection against the effects of shock and vibration.

External Shock and Vibration Mitigation

The key to protecting electronic systems from the effects of extreme shock and vibration however is in limiting the transfer of those forces to the chassis in the first place. Shock and vibe management begins outside the chassis in the form of isolation systems that help to prevent the transfer of damaging forces to sensitive electronics.

Wire Rope Isolators

Metal wire rope isolators are by far the most widely applied solutions to shock and vibration in the DoD.  They can be used across all forms of electronic packaging, ranging from smaller ATR style chassis to 19” rackmount chassis in full rackmount systems. Shock qualified solutions for all branches of the military are designed and tuned for ground, air and sea-based assets. COTS and custom solutions are adapted to address the frequency, duration, magnitude and directional forces along with the size, weight and materials of the system. A tuned system of separate isolators may be placed on the chassis at the individual points of attachment to the vehicle.

Shock isolators from LCR and Isolation Dynamics Corp can be custom fitted for a broad range of shock and vibration protection for ATR’s in ground vehicles up to complete rack systems on naval ships and large air frames. 

COTS and Custom Shock Trays

Alternately, shock trays with standardized mounting options and built in isolators provide isolation for chassis in a single chassis/tray assembly. For ATR and Standard A-Kit/Vehicle Envelope (SAVE) compliant electronic systems, LCRs shock and isolation trays are COTS solution for army ground vehicles. The trays utilize the SINCGAR hole pattern with optional configurations that accommodate both wire rope isolators and cupmount isolators for a broader range of control over shock and vibration attenuation in a wide range of applications.

Protecting critical electronics against the harmful effects of shock and vibration in defense applications takes many forms. PC boards, connectors and components in VPX/SOSA aligned systems can withstand battlefield operating conditions through rugged packaging design using heavy duty construction techniques and materials along with shock isolation solutions that mitigate the transfer of excessive forces to the system.